A network device typically includes a plurality of ports coupled to different network links. The network device receives packets via ones of the ports and processes address information in a header of a received packet to decide via which other port or ports the network device should transmit the packet. While the network device performs processing of the packets and until egress interfaces are ready to transmit the packets, the packets are temporarily stored in an internal memory of the network device. When a determined port is available for transmission of a packet, the packet is retrieved from the internal memory and transmitted via the port.
In some situations, a downstream network device in a switching system receives packets from one or more upstream network devices in the switching system faster than the packets can be transmitted via at least some egress ports of the downstream network device. In such situations, the downstream network device (e.g., internal memory of the downstream network device) becomes congested due to an insufficiently high transmission rate of packets via the at least some egress ports of the downstream network device. To prevent loss of packets in case of congestion at the downstream network device, the downstream network device generates flow control messages that are subsequently transmitted to an upstream network device to thereby cause the upstream network device to modulate the flow of packets to the downstream network device. As an example, the upstream network device temporarily reduces the rate of transmission of packets to the network device to thereby alleviate congestion at the downstream network device. In a typical switching system, such flow control messages cause the upstream network device to modulate the flow of all packets to the downstream network device regardless of the egress ports of the downstream network device to which the packets are to be subsequently directed at the downstream network device. As a result, congestion at one egress port of the downstream network device unnecessarily causes flow control (e.g., reduction of transmission rate) of packets directed to other non-congested egress ports of the downstream network device.